virt: Adds support for kernel extra params

kernel_extra_params = " ..."

Signed-off-by: Jiří Župka <jzupka@redhat.com>
virt: Adds timedrift test without network interface.

test:
   guest_suspend
   guest_pause_resume

Signed-off-by: Jiří Župka <jzupka@redhat.com>